Light transmitting plate

ABSTRACT

A light guide plate of the present invention is characterized by being obtained by melt molding a thermoplastic resin having a melt flow rate of at least 50 [g/10 min.] under a load of 2.16 kgf at 280° C. 
     The thermoplastic resin is preferably a thermoplastic resin containing an alicyclic structure, more preferably a norbornene-based polymer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light guide plate, more particularlyto a light guide plate with an excellent appearance and redecedirregularity in luminance, in particular a thin-walled, large screensize light guide plate.

2. Description of the Related Art

A light guide plate is one optical member used in a backlight unitmounted in various display devices. For example, an edge light typeplanar light source device is generally comprised of a light guide platefor guiding light from a light source entering from a side end face in adirection parallel to the plate face and causing it to be emitted in adirection substantially perpendicular to the plate face, a reflectorarranged so as to surround the light source for efficiently guiding thelight of the light source not directly entering the light source-sideend face of the light guide plate, a light diffusion sheet or platearranged at the light emitting face side of the light guide plate forcausing diffusion of light emitted from the emission face, and areflection sheet or plate arranged at the light reflection face side ofthe light guide plate for returning the light leaked from the lightguide plate to the light guide plate once again.

Note that the back face of the light guide plate (light reflection face)is formed with a pattern of various shapes such as dots, cone cuts, andV-grooves for raising or uniformly diffusing the luminance of the lightintroduced into the light guide plate.

The light guide plate has to have redeced irregularity in luminancesince the entire emission face serves as the direct light source ofvarious types of display devices. Further, it is believed desirable thatthe color temperature be high. Therefore, in the past, use has been madeof a light guide plate made by injection molding a colorless transparentthermoplastic resin such as polymethyl methacrylate (PMMA) orpolycarbonate (PC). Further, recent light guide plates have tended to bemade thinner from the viewpoint of increasing the screen size oreconomizing the space.

The PMMA normally used for molding a light guide plate, however, has ahigh melt viscosity at the time of injection molding and inferiorfluidity and is difficult to mold into a thin-walled, large screen sizeof over 10 inches, further over 14 inches. Even if able to be molded,since it is thin, there was the problem that hygroscopic deformationended up occurring. On the other hand, if the resin temperature israised to improve the fluidity, the resin is liable to foam in thecylinder and a shaped article with a good appearance is difficult toobtain such as due to the occurrence of voids. Further, since PC has ahigh heat deformation temperature, the molding temperature has to beraised in order to obtain a fluidity sufficient for molding thinarticles. As a result, due to the effects of moisture absorption, theresin is liable to hydrolyze and foam in the cylinder. In the same wayas the case of PMMA, voids occurred in the shaped article (light guideplate) and it was difficult to obtain a shaped article with a goodappearance. Therefore, a molding material has been sought which enablesmolding of a thin-walled light guide plate of a large screen size ofover 10 inches or over 14 inches with a good appearance by injectionmolding.

Further, when using PMMA or PC as the molding material and formingV-grooves etc. in the back face of the light guide plate, there has beenthe problem that it was not possible to precisely transfer the patternof the fine shapes to the light reflection face side of the thinnestpart, that is, the narrow end portion, in a wedge-shaped light guideplate where the thickness of the light guide plate becomes graduallythinner the further from the light source. This becomes a cause of areduction of the homogenity of the light emitted due to luminanceunevenness.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a light guide plate ofa good appearance and redeced irregularity in luminance, in particular athin-walled, large screen size light guide plate, and a process forproduction of the same.

The present inventors took note of the melt fluidity of a thermoplasticresin and engaged in intensive studies with the aim of improving it. Asa result, they discovered that by melt molding a thermoplastic resinhaving a specific melt flow rate (hereinafter also referred to as an“MFR”), it is possible to obtain a light guide plate with a goodappearance and redeced irregularity in luminance, in particular athin-walled, large screen size light guide plate, and thereby completedthe present invention.

A light guide plate according to the present invention is characterizedby being obtained by melt molding a thermoplastic resin having a meltflow rate of at least 50 [g/10 min.] under a load of 2.16 kgf at 280° C.

A process of production of a light guide plate according to the presentinvention is characterized by melt molding a thermoplastic resin havinga melt flow rate of at least 50 [g/10 min.] under a load of 2.16 kgf at280° C.

Effects

According to the present invention, there is provided a light guideplate with a good appearance and redeced irregularity in luminance, inparticular a thin-walled, large screen size (for example, at least 10inches size, preferably at least 14 inches size) light guide plate, anda process for production of the same.

In particular, a thermoplastic resin having an MFR of at least 50 [g/10min.] has a low viscosity. Therefore, according to the present inventionusing such a resin, the melt fluidity of the resin at the time of meltmolding can be improved and a shaped article (light guide plate) havinga good appearance can be obtained. In particular, if a resin with a lowviscosity is used when molding a thin-walled, large screen light guideplate, fluidization and plastization become possible even at a lowtemperature and cooling and solidification become easy. Further, sincethe melt fluidity is good, it is possible to precisely transfer even apattern of fine shapes such as V-grooves to the reflection face side ofthe light guide plate. Further, the cycle time at the time of molding iscomparatively short, the productivity of the light guide plate rises,the residence time in the molten state becomes shorter, and the rate ofoccurrence of voids, burn marks, and discoloration falls. Therefore, itbecomes easy to obtain a light guide plate with a good appearance andredeced irregularity in luminance even when producing a thin-walled,large screen size (for example, at least 10 inches size or at least 14inches size) light guide plate.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of the preferredembodiments given with reference to the attached drawings, in which:

FIG. 1A is a perspective view showing the outline of a planar lightsource device including a light guide plate of the present embodiment;

FIG. 1B is a sectional view along the line IB—IB of FIG. 1A;

FIG. 1C is an enlarged view of principal parts of FIG. 1B;

FIG. 1D is a partially enlarged view of the reflection face of FIG. 1C;

FIG. 2A to FIG. 2E are views for explaining the process of production ofa light guide plate of the present embodiment;

FIG. 3A is a right side view of a light guide plate produced by theprocess of FIG. 2A to FIG. 2E; and

FIG. 3B is a bottom view of FIG. 3A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, the light guide plate according to the present invention will beexplained based on the following embodiments.

These embodiments, however, are described for the purpose offacilitating understanding of the present invention and are notdescribed for limiting the present invention.

Thermoplastic Resin

As the thermoplastic resin used in the present invention, athermoplastic resin having a specific MFR is used.

Specifically, the MFR of the thermoplastic resin is at least 50 [g/10min.], preferably 50 to 250 g/min, more preferably 60 to 180 [g/10min.]. When the MFR of the thermoplastic resin is excesssively low, themoldability is poor, so this is not preferable. Further, when converselyit is excessively high, the mechanical strength is inferior, athin-walled, large screen size light guide plate is hard to produce, andthe moldability is inferior such as with occurrence of burrs.

The thermoplastic resin used in the present invention is notparticularly limited as to its 50% breaking energy in a drop-weight testmeasured for a 3 mm thick plate of the same using a missile-type weightof a radius of ¾ inch, but preferably is at least 0.1 J, more preferablyat least 0.05 J. The mechanical strength of the light guide plateobtained at the time of this range is suitably held even if the lightguide plate is thin and has a large screen size. Further, it isresistant to occurrence of cracks or fractures and can be easilyassembled into backlight units.

The glass transition temperature (Tg) of the thermoplastic resin used inthe present invention may be suitably selected in accordance with theobject of use, but a higher one is preferable from the environment ofuse of the light guide plate. Normally, it is at least 70° C.,preferably 70 to 250° C., more preferably 80 to 200° C. In this range,the properties of the heat resistance and moldability are well balanced.

The refractive index at 25° C. of the thermoplastic resin used in thepresent invention may be suitably selected in accordance with the objectof use, but preferably is 1.40 to 1.70, more preferably 1.50 to 1.60,still more preferably 1.52 to 1.56. The optical characteristics aredesirable in this range.

As the thermoplastic resin used in the present invention, for example,polymethyl methacrylate, polyethyl methacrylate, poly-n-propylmethacrylate, poly-n-butyl methacrylate, poly-n-hexyl methacrylate,polyisopropyl methacrylate, polyisobutyl methacrylate, poly-t-butylmethacrylate, polybenzyl methacrylate, polyphenyl methacrylate,poly-1-phenylethyl methacrylate, poly-2-phenylethyl methacrylate,polyfurfuryl methacrylate, polymethyl acrylate, polyethyl acrylate,poly-n-butyl acrylate, polybenzyl acrylate, poly-2-chlorethyl acrylate,polyvinyl acetate, polyvinyl benzoate, polyvinylphenyl acetate,polyacrylonitrile, poly-α-methylacrylonitrile,polymethyl-α-chloracrylate, poly-o-chlorstyrene, poly-p-fluorostyrene,poly-p-isopropylstyrene, polystyrene, polycarbonate, thermoplastic resincontaining an alicyclic structure, etc. may be mentioned.

These thermoplastic resins may be used alone or in combinations of twoor more types.

Among the above thermoplastic resins, from the viewpoint of the ease ofmolding of a thin-walled, large screen size light guide plate, athermoplastic resin containing an alicyclic structure is preferred. Theheat decomposition temperature of a thermoplastic resin containing analicyclic structure is high, so by using such a resin, the moldabilityis further improved. In particular, it becomes possible to mold withoutheat decomposition or hydrolysis even at a high temperature. A lightguide plate with a good appearance can therefore be obtained. Further,since the melt fluidity is improved, there is less of a liability oftransfer defects arising even when forming a pattern of fine shapes suchas V-grooves in the reflection face of the light guide plate. Further,even when producing a thin-walled, large screen size light guide platehaving heat resistance, having grooves as a pattern of fine shapes, itis possible to obtain a light guide plate redeced irregularity inluminance. Further, an alicyclic-structure containing thermoplasticresin is superior in transparency or heat resistance, so can be furtherimproved in luminance. Even if the light guide plate is used for a longtime, there is less liability of occurrence of deformation due tochanges in temperature. This makes it suitable for application as alight guide plate.

The alicyclic-structure containing thermoplastic resin has alicyclicstructures at its main chain and/or side chains. From the viewpoint ofthe mechanical strength, heat resistance, etc., one containing alicyclicstructures at its main chain is preferable.

As the alicyclic structures of the polymer, saturated cyclic hydrocarbonstructures, unsaturated cyclic hydrocarbon structures, etc. may bementioned, but from the viewpoint of mechanical strength and heatresistance, cycloalkane structures or cycloalkene structures arepreferable. In particular, a thermoplastic resin having cycloalkanestructures is most preferable.

The number of carbon atoms making up the alicyclic structures is notparticularly limited, but is usually 4 to 30, preferably 5 to 20, morepreferably 5 to 15. In this range, the properties of the mechanicalstrength, heat resistance, and moldability are well balanced.

The ratio of the monomers giving repeating units of alicyclic structuresin the thermoplastic resin containing an alicyclic structure used in thepresent invention may be suitably selected in accordance with the objectof use, but normally is at least 40 mol %, preferably at least 50 mol %.If the ratio of monomers giving repeating units of alicyclic structuresin the alicyclic structure-containing thermoplsatic resin is excessivelysmall, the heat resistance is inferior. By making the range from 40 to100 mol %, the transparency, mechanical strength, heat resistance, etc.are well balanced.

The balance of the thermoplastic resin containing an alicyclic structureother than the repeating units having the alicyclic structure is notparticularly limited and may be suitably selected in accordance with theobject of use.

As specific examples of such a thermoplastic resin containing analicyclic structure, for example, (1) norbornene-based polymers, (2)monocyclic cyclic olefin-based polymers, (3) cyclic conjugateddiene-based polymers, (4) vinyl alicyclic hydrocarbon-based polymers,etc. may be mentioned. Among these, norbornene-based polymers and cyclicconjugated diene-based polymers are preferable, while norbornene-basedpolymers are more preferable. When a norbornene-based polymer is used,the stability of appearance of the obtained light guide plate becomesmuch more remarkable, the occurrence of luminance unevenness is greatlyreduced, and a high mechanical strength is imparted to the light guideplate. Therefore, even if molding a thin-walled light guide plate with alarge screen size, the new effect is obtained that cracks or fracturesare difficult to occur and assembly into a backlight unit becomes easy.

(1) Norbornene-Based Polymers

The norbornene-based polymers are not particularly limited, but forexample the polymers disclosed in Japanese Unexamined Patent Publication(Kokai) No. 2-173112, Japanese Unexamined Patent Publication (Kokai) No.3-14882, Japanese Unexamined Patent Publication (Kokai) No. 5-9223,Japanese Unexamined Patent Publication (Kokai) No. 3-122137, etc. may beused.

Specifically, ring-opening polymers of norbornene-based monomers andtheir hydrogenates, addition type (co)polymers of norbornene-basedmonomers, addition-type copolymers of norbornene-based monomers andvinyl-based compounds able to be copolymerized with the same, etc. maybe mentioned. Among these, ring-opening polymers of norbornene-basedmonomers and their hydrogenates, addition type polymers ofnorbornene-based monomers, and addition-type copolymers ofnorbornene-based monomers and vinyl-based compounds able to becopolymerized with the same are preferable in balancing the heatresistance and moldability.

As the norbornene-based monomers, for example, bicyclo[2,2,1]hept-2-ene(commonly called “norbornene”), 5-methyl-bicyclo[2,2,1]hept-2-ene,5,5-dimethyl-bicyclo[2,2,1[hept-2-ene, 5-ethyl-bicyclo[2,2,]hept-2-ene,5-butyl-bicyclo[2,2,1]hept-2-ene, 5-ethylidene-bicyclo[2,2,1]hept-2-ene,5-hexyl-bicyclo[2,2,1]hept-2-ene, 5-octyl-bicyclo[2,2,1]hept-2-ene,5-octadecyl-bicyclo[2,2,1]hept-2-ene,5-ethylidene-bicyclo[2,2,1]hept-2-ene,5-methylidene-bicyclo[2,2,1]hept-2-ene,5-vinyl-bicyclo[2,2,1]hept-2-ene, 5-propenyl-bicyclo[2,2,1]hept-2-ene,5-methoxycarbonyl-bicyclo[2,2,1]hept-2-ene,5-cyano-bicyclo[2,2,1]hept-2-ene,5-methyl-5-methoxycarbonyl-bicyclo[2,2,1]hept-2-ene; 5-methoxycarbonylbicyclo[2,2,1]hept-2-ene, 5-ethoxycarbonyl bicyclo[2,2,1]hept-2-ene,5-methyl-5-methoxycarbonyl bicyclo[2,2,1]hept-2-ene,5-methyl-5-ethoxycarbonyl bicyclo[2,2,1]hept-2-ene,bicyclo[2,2,1]hept-5-enyl-2-methylpropionate,bicyclo[2,2,1]hept-5-enyl-2-methyloctanate,bicyclo[2,2,1]hept-2-ene-5,6-dicarboxylic acid anhydride,5-hydroxymethyl bicyclo[2,2,1]hept-2-ene,5,6-di(hydroxymethyl)bicyclo[2,2,1]hept-2-ene,5-hydroxy-i-propylbicyclo[2,2,1]hept-2-ene, 5,6-dicarboxybicyclo[2,2,1]hept-2-ene; 5-cyanobicyclo[2,2,1]hept-2-ene,bicyclo[2,2,1]hept-2-ene-5,6-dicarboxylic acid imide;

tricyclo[4,3,0,1^(2,5)]deca-3,7-diene (commonly called“dicyclopentadiene”), tricyclo[4,3,0,1^(2,5)]deca-3-ene;tricyclo[4,4,0,1^(2,5)]undeca-3,7-diene ortricyclo[4,4,0,1^(2,5)]undeca-3,8-diene or their partial hydrogenates(or adducts of cyclopentadiene andcyclohexene)tricyclo[4,4,0,1^(2,5)]undeca-3-ene;5-cyclopentyl-bicyclo[2,2,1]hept-2-ene,5-cyclohexyl-bicyclo[2,2,1]hept-2-ene,5-cyclohexenyl-bicyclo[2,2,1]hept-2-ene,5-phenyl-bicyclo[2,2,1]hept-2-ene;

tetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene (also simply calledtetracyclododecene),8-methyltetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene8-ethyltetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-methylidenetetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-ethylidenetetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-vinyltetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-propenyl-tetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-methoxycarbonyltetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-methyl-8-methoxycarbonyltetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-hydroxymethyltetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-carboxytetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene;8-cyclopentyl-tetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-cyclohexyl-tetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-cyclohexenyl-tetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene,8-phenyl-cyclopentyl-tetracyclo[4,4,0,1^(2,5),1^(7,10)]-dodeca-3-ene;

tetracyclo[4,4,0,1^(10,13),0^(2,7)]trideca-2,4,6,11-tetraene (alsocalled “1,4-methane-1,4,4a,9a-tetrahydrofluorene”),tetracyclo[4,4,0,1^(11,14),0^(3,8)]-tetradeca-3,5,7,12-tetraene (alsocalled “1,4-methane-1,4,4a,5,10,10a-hexahydroanthracene”),pentacyclo-[6,5,1,1^(3,6),0^(2,7),0^(9,13)]pentadeca-3,10-diene,pentacyclo[7,4,0,1^(3,6),1^(10,13),0^(2,7)]pentadeca-4, 11-diene;tetramers of cyclopentadiene; and other norbornene-based monomers etc.may be mentioned.

These norbornene-based monomers may be used alone or in combinations oftwo or more types.

As the vinyl-based compounds able to be copolymerized with thenorbornene-based monomers, in particular chain-like vinyl compounds aresuitable in increasing the heat resistance or transparency.Specifically, ethylene, propylene, 1-butene, 1-pentene, 1-hexene,3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene,4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene,4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene,1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene,1-eicocene, and other C₂ to C₂₀ ethylene or α-olefin; cyclobutene,cyclopentene, cyclohexene, 3,4-dimethylcyclopentene,3-methylcyclohexene, 2-(2-methylbutyl)-1-cyclohexene, cyclooctene,3a,5,6,7a-tetrahydro-4,7-methano-1H-indene, and other cycloolefins;1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene,1,7-octadiene, and other nonconjugated dienes; etc. may be mentioned.

These vinyl-based compounds may be used alone or in combinations of twoor more types.

The ratio of the norbornene-based monomer and the vinyl compound may besuitably selected in accordance with the object of use, but the molarratio (norbornene-based monomer/vinyl compound) is usually 40/60 to100/0, preferably 50/50 to 100/0. When this, the mechanical strength,heat resistance, and transparency of the light guide plate are wellbalanced.

The ring-opening polymerization of the norbornene-based monomer ornorbornene-based monomer and vinyl-based compound able to becopolymerized with this usually may be performed in the presence of aring-opening polymerization catalyst and molecular weight adjustingagent. As the ring-opening polymerization catalyst, for example,catalyst systems comprised of halides, nitrates, or acetylacetonecompounds of ruthenium, rhodium, palladium, osmium, iridium, platinum,and other metals and reducing agents or catalyst systems comprised ofhalides or acetylacetone compounds of metals such as titanium, vanadium,zirconium, tungsten, and molybdenum and organoaluminum compounds may bementioned. As the molecular weight adjusting agent, normally achain-like monoolefin or chain-like conjugated dienes are used, but forexample, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene,1-dodecene, 1,4-hexadiene, etc. may be mentioned. The amount of themolecular weight adjusting agent used is suitably selected according tothe polymerization conditions, but usually is, in terms of a molar ratiowith respect to the total monomers, 1/10 to 1/500, preferably 1/25 to1/250, more preferably 1/50 to 1/200. When in this range, the molecularweight is easy to control and the MFR becomes easy to control. As themethod of addition of a molecular weight adjusting agent, for additionto the reaction system at a high accuracy, it is preferable to use itdiluted by a reaction solvent etc. in advance or add it using anapparatus with a high measurement accuracy. As the accuracy of theamount of the molecular weight adjusting agent added, normally the rangeof error of the amount added required for the desired molecular weightis not more than 3%, preferably not more than 2%, more preferably notmore than 1%. At this time, the molecular weight can be easilycontrolled and the MFR can be easily controlled. The ring-openingpolymerization reaction may be performed in a solvent or not in thepresence of a solvent at a polymerization temperature of −50 to 100° C.and a polymerization pressure of 0 to 50 kg/cm².

A hydrogenate of the ring-opening polymer of the norbornene-basedmonomer may be produced by an ordinary method. Specifically, it may beobtained by hydrogenation of a polymerization solution of a ring-openingpolymer of the above norbornene-based monomer in the presence of ahydrogenation catalyst. The hydrogenation catalyst is not particularlylimited, but normally a nonhomogeneous catalyst or homogeneous catalystis used. As the nonhomogeneous catalyst, for example, nickel, palladium,platinum, or nickel/silica, nickel/diatomaceous earth, nickel/alumina,palladium/carbon, palladium/silica, palladium/diatomaceous earth,palladium/alumina, etc. may be mentioned. As the homogeneous catalyst,for example, a catalyst comprised of a combination of a transition metalcompound and alkylaluminum metal compound or alkyllithium, for example,a catalyst comprised of a combination of cobaltacetate/triethylaluminum, cobalt acetate/triisobutyl-aluminum, nickelacetate/triethylaluminum, nickel acetate/triisobutylaluminum, nickelacetylacetnate/tri-ethylaluminum, nickelacetylacetnate/triisobutyl-aluminum, titanocene chloride/n-butyllithium,zirconocene chloride/n-butyllithium, etc. may be mentioned. Thesehydrogenated catalysts may be used alone or in combinations of two ormore types. The amount of the hydrogenated catalyst used is normally0.01 to 100 parts by weight, preferably 0.1 to 50 parts by weight, morepreferably 1 to 30 parts by weight with respect to 100 parts by weightof a ring-opening polymer of a norbornene-based monomer. Thehydrogenation reaction is normally performed under a hydrogen pressureof 1 to 150 kg/cm², a temperature range of 0 to 250° C., and a reactiontime of 1 to 20 hours.

Addition (co)polymers of norbornene-based monomers and addition typecopolymers of norbornene-based monomers and vinyl-based compounds ableto be copolymerized with the same may be obtained by the method of forexample polymerizing the monomer ingredients at a polymerizationtemperature of usually −50 to 100° C. and a polymerization pressure of 0to 50 kg/cm² in a solvent or not in a solvent in the presence of acatalyst system comprised of a titanium, zirconium, or vanadium compoundand organoaluminum compound.

(2) Monocyclic Cyclic Olefin-Based Polymers

As the monocyclic cyclic olefin-based polymers, for example, use may bemade of addition polymers of cyclohexene, cycloheptene, cyclooctene, andother monocyclic cyclic olefin-based monomers disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 64-66216.

(3) Cyclic Conjugated Diene-Based Polymers

As the cyclic conjugated diene-based polymers, for example, use may bemade of polymers obtained by 1,2- or 1,4-addition polymerization ofcyclopentadiene, cyclohexadiene, and other cyclic conjugated diene-basedmonomers and their hydrogenates disclosed at Japanese Unexamined PatentPublication (Kokai) No. 6-136057 or Japanese Unexamined PatentPublication (Kokai) No. 6-258318.

(4) Vinyl Alicyclic Hydrocarbon-Based Polymers

As the vinyl alicyclic hydrocarbon-based polymers, for example, polymersof vinyl cyclohexene, vinyl cyclohexane, and other vinyl alicyclichydrocarbon-based monomers and their hydrogenates disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 51-59989, hydrogenates ofaromatic ring portions of polymers of vinyl aromatic monomers such asstyrene and α-methylstyrene disclosed in Japanese Unexamined PatentPublication (Kokai) No. 63-43910, Japanese Unexamined Patent Publication(Kokai) No. 64-1706, etc. may be used.

The weight average molecular weight (Mw) of the alicyclicstructure-containing thermoplastic is, converted to polyisoprene by highpressure liquid chromatography using cyclohexane as a mobile phase,normally 10,000 to 100,000, preferably 13,000 to 70,000, more preferably14,000 to 60,000, particularly preferably 15,000 to 50,000. When the Mwis in this range, the mechanical strength and moldability of the lightguide plate obtained are well balanced.

Further, the molecular weight distribution (MWD), expressed by the ratio(Mw/Mn) of Mw and the number average molecular weight of the alicyclicstructure-containing thermoplastic resin, is usually not more than 4.0,preferably not more than 3.0, more preferably not more than 2.7,particularly preferably not more than 2.5. When the molecular weightdistribution is in this range, the mechanical strength and moldabilityof the light guide plate obtained are well balanced.

These thermoplastic resins including an alicyclic structure may be usedalone or in combinations of two or more types.

Other Ingredients

The thermoplastic resin for molding the “light guide plate” according tothe present invention may, as needed, include a soft polymer and varioustypes of compounding agents alone or in mixtures of two or more types.

(1) Soft Polymers

In the present invention, the soft polymer to be blended into thethermoplastic resin usually means a polymer having a glass transitiontemperature (Tg) of not more than 30° C. In the case of a polymer havingseveral Tg's, any polymer having a lowest Tg of not more than 30° C. isincluded in such a soft polymer.

As such a soft polymer, (a) an olefin-based soft polymer mainlycomprised of ethylene, propylene, or another α-olefin, (b) anisobutylene-based soft polymer mainly comprised of isobutylene, (c) adiene-based soft polymer mainly comprised of butadiene, isoprene, oranother conjugated diene, (d) a soft polymer having silicon-oxygen bondsas skeletons (organic polysiloxane), (e) soft polymers mainly comprisedof α,β-unsaturated acids and their derivatives, (f) soft polymers mainlycomprised of unsaturated alcohols and amines or their acyl derivativesor acetal, (g) polymers of epoxy compounds, (h) fluorine-based rubber,(i) other soft polymers, etc. may be mentioned.

As specific examples of these soft polymers, for example, as (a), liquidpolyethylene, atactic polypropylene, 1-butene, 4-methyl-1-butene,1-hexene, 1-octene, and 1-decene and other homo polymers;ethylene-α-olefin copolymers, propylene-α-olefin copolymers,ethylene-propylene-diene copolymers (EPDM), ethylene-cyclic olefincopolymers, ethylene-propylene-styrene copolymers, and other copolymersmay be mentioned.

As (b), polyisobutylene, isobutylene-isoprene rubber,isobutylene-styrene copolymers, etc. may be mentioned.

As (c), polybutadiene, polyisoprene, and other conjugated diene homopolymers; a butadiene-styrene random copolymer, isoprene-styrene randomcopolymer, acrylonitrile-butadiene copolymer, a hydrogenate of anacrylonitrile-butadiene copolymer, an acrylonitrile-butadiene-styrenecopolymer, and other random copolymers of conjugated dienes; abutadiene-styrene block copolymer, styrene-butadiene-styrene blockcopolymer, isoprene-styrene block copolymer, styrene-isoprene-styreneblock copolymer, and other block copolymers of conjugated dienes andaromatic vinyl-based hydrocarbons and their hydrogenates may bementioned.

As (d), dimethyl polysiloxane, diphenyl polysiloxane, dihydroxypolysiloxane, and other silicone rubbers etc. may be mentioned.

As (e), polybutyl acrylate, polybutyl methacrylate, polyhydroxyethylmethacrylate, polyacrylamide, polyacrylonitrile, and other acryl monomerhomo polymers; butylacrylate-styrene copolymers, and other copolymers ofacryl monomers and other monomers may be mentioned.

As (f), polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate,polyvinyl benzoate, polyvinyl maleate, and other (esterified)unsaturated alcohol homo polymers; vinyl acetate-styrene copolymers andother copolymers of (esterified) unsaturated alcohols and other monomersmay be mentioned.

As (g), polyethylene oxide, polypropylene oxide, epichlorohydrin rubber,etc. may be mentioned.

As (h), vinylidene fluoride based rubber, ethylenetetrafluoride-propylene rubber, etc. may be mentioned.

As (i), natural rubber, polypeptide, protein, and the polyester-basedthermoplastic elastomer, vinyl chloride-based thermoplastic elastomer,polyamide-based thermoplastic elastomer, etc. disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 8-73709, etc. may bementioned. These soft polymers may have cross-linked structures or mayhave functional groups introduced by modification.

These soft polymers may be used alone or in mixtures of two or moretypes. Further, the ratio may be suitably selected within the range notdetracting from the object of the present invention.

(2) Compounding Agent

As specific examples of the above various compounding agents, the agentsare not particularly limited so long as they are ones generally used inthe plastic industry. For example, an antioxidant, UV absorbent,photostabilizer, near infrared absorbent, dye, pigment, or othercoloring agent, lubricant, softening agent, anti-static agent,fluorescent brightening agent, filler, or other compounding agent may bementioned.

As the antioxidant, a phenol-based antioxidant, phosphorus-basedantioxidant, sulfur-based antioxidant, etc. may be mentioned. Amongthese, a phenol-based antioxidant is preferable. An alkyl-substitutedphenol-based antioxidant is particularly preferable.

As the phenol-based antioxidant, conventionally known ones may be used.For example,2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate,2,4-di-t-amyl-6-(1-(3,5-di-t-amyl-2-hydroxphenyl)ethyl)phenylacrylate,and other acrylate-based compounds described in Japanese UnexaminedPatent Publication (Kokai) No. 63-179953 or Japanese Unexamined PatentPublication (Kokai) No. 1-168643;octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2,2′-methylene-bis(4-methyl-6-t-butylphenol),1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,1,3,5-trimethyl-2,4,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,tetrakis(methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenylpropionate)methane[that is,pentaerythrimethyl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenylpropionate)],triethyleneglycol bis(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate),and other alkyl-substituted phenol-based compounds;6-(4-hydroxy-3,5-di-t-butylanilino)-2,4-bisoctylthio-1,3,5-triazine,4-bisoctylthio-1,3,5-triazine,2-octylthio-4,6-bis-(3,5-di-t-butyl-4-oxyanilino)-1,3,5-triazine, orother triazine base-containing phenol-based compounds, etc. may bementioned.

The phosphorus-based antioxidant is not particularly limited so long asit is one which is usually used in the general plastics industry. Forexample, triphenylphosphate, diphenylisodecyl-phosphate,phenyldiisodecylphosphate, tris(nonylphenyl)phosphate,tris(dinonylphenyl)-phosphate, tris(2,4-di-t-butylphenyl)phosphate,10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide,and other monophosphate-based compounds;4,4′-butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecylphosphate),4,4′isopropylidene-bis(phenyl-di-alkyl(C₁₂ to C₁₅) phosphate), and otherdiphosphate-based compounds etc. may be mentioned. Among these, amonophosphate-based compound is preferable. Tris(nonylphenyl)phosphate,tris(dinonylphenyl)phosphate, tris(2,4-di-t-butylphenyl)phosphate, etc.are particularly preferred.

As the sulfur-based antioxidant, for example, dilauryl3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl3,3-thiodipropionate, laurylstearyl 3,3-thiodipropionate,pentaerythritol-tetrakis-(β-lauryl-thio-propionate,3,9-bis(2-dodecylthicethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, etc.may be mentioned.

These antioxidants may be used alone or in combinations of two or moretypes. The amount of the antioxidant blended is suitably selected withina range not detracting from the object of the present invention, butnormally is 0.001 to 5 parts by weight, preferably 0.01 to 1 part byweight with respect to 100 parts by weight of the thermoplastic polymerresin.

As the UV absorbent, for example,2-(2-hydroxy-5-methylphenyl)2H-benzotriazole,2-(3-t-butyl-2-hydroxy-5-methylphenyl)-5-chloro-2H-benzotriazole,2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chloro-2H-benzotriazole,2-(3,5-di-t-butyl-2-hydroxyphenyl)-2H-benzotriazole,5-chloro-2-(3,5-di-t-butyl-2-hydroxyphenyl)-2H-benzotriazole,2-(3,5-di-t-amyl-2-hydroxyphenyl)-2H-benzotriazole, and otherbenzotriazole-based UV absorbents;

4-t-butylphenyl-2-hydroxybenzoate, phenyl-2-hydroxybenzoate,2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate,hexadecyl-3,5-di-t-butyl-4-hydroxybenzoate,2-(2H-benzotriazol-2-yl)-4-methyl-6-(3,4,5,6-tetrahydrophthalimidylmethyl)phenol,2-(2-hydroxy-5-t-octylphenyl)-2H-benzotriazole,2-(2-hydroxy-4-octylphenyl)-2H-benzotriazole, and other benzoate-basedUV absorbents;

2,4-dihydroxybenzophenone, 2-hydroxy-4-methylbenzophenone,2-hydroxy-4-methoxybenzophenone-5-sulfonate 3-hydrate,2-hydroxy-4-octyloxybenzophenone, 4-dodecaloxy-2-hydroxybenzophenone,4-benzyloxy-2-hydroxybenzophenone, 2,2′,4,4′-tetrahydroxy-benzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzo-phenone, and other benzophenone-basedUV absorbents;

ethyl-2-cyano-3,3-diphenylacrylate,2′-ethylhexyl-2-cyano-3,3-diphenylacrylate, and other acrylate-based UVabsorbents; nickel [2,2′-thiobis(4-t-octylphenolate)]-2-ethylhexylamine,and other metal complex-based UV absorbents etc. may be mentioned.

As photostabilizers, for example,2,2,6,6-tetramethyl-4-piperidylbenzoate,bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate,4-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy)-1-(2-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy)ethyl)-2,2,6,6-tetramethylpiperidine,and other hindered amine-based photostabilizers may be mentioned.

As the near infrared absorbent, for example, cyanine-based near infraredabsorbents; pyrylium-based infrared absorbents; squalilium-based nearinfrared absorbents; croconium-based UV absorbents; azulenium-based nearinfrared absorbents; phthalocyanine-based near infrared absorbents;dithiol metal complex-based near infrared absorbents;naphthoquinone-based near infrared absorbents; anthraquionene-based nearinfrared absorbents; indophenol-based near infrared absorbents;azi-based near infrared absorbents; etc. may be mentioned. Further, thecommercially available near infrared absorbents SIR-103, SIR-114,SIR-128, SIR-130, SIR-132, SIR-152, SIR-159, SIR-162 (all made by MitsuiToatsu Dyes), Kayasorb IR-750, Kayasorb IRG-002, Kayasorb IRG-003,IR-820B, Kayasorb IRG-022, Kayasorb IRG-023, Kayasorb CY-2, KayasorbCY-4, Kayasorb CY-9 (all made by Nippon Kayaku), etc. may be mentioned.

The dyes are not particularly limited so long as they are ones whichuniformly disperse and dissolve in thermoplastic resins including analicyclic structure, but broad use is made of oil-soluble dyes (variousCI solvent dyes) since they are superior in solubility with thethermoplastic hydrocarbon-based polymers used in the present invention.As specific examples of oil-soluble dyes, the various types of CIsolvent dyes described in Color Index, vol. 3 of the Societ of Dyes andColourists may be mentioned.

As pigments, for example, Pigment Red 38 and other dianilide-basedpigments; Pigment Red 48:2, Pigment Red 53, Pigment Red 57:1, and otherazo lake-based pigments; Pigment Red 144, Pigment Red 166, Pigment Red220, Pigment Red 221, Pigment Red 248, and other condensation azo-basedpigments; Pigment Red 171, Pigment Red 175, Pigment Red 176, Pigment Red185, Pigment Red 208, and other benzimidazolone-based pigments; PigmentRed 122 and other quinacridone-based pigments; Pigment Red 149, PigmentRed 178, Pigment Red 179, and other perillene-based pigments; andPigment Red 177 and other anthraquinone-based pigments may be mentioned.

When the light guide plate produced by the process of the presentinvention requires coloring, both a dye and pigment can be used withinthe range of the object of the present invention and are not limited,but coloring by a dye is preferable in the case of a light guide platewhere microoptical characteristics become a problem. Further, a UVabsorbent sometimes appears yellow to red to the eye, while a nearinfrared absorbent sometimes appears black to the eye. Therefore, thereis no need for strictly differentiating between these and dyes in use.Further, they may be used together.

As the lubricant, an ester of an aliphatic alcohol, an ester of apolyhydric alcohol, or a partial ester or other organic compound orinorganic particles etc. may be used. As organic compounds, for example,glyceryl monostearate, glyceryl monolaurate, glyceryl distearate,pentaerythritol monostearate, pentaerythritol distearate,pentaerythritol tristearate, etc. may be mentioned.

As other lubricants, generally it is possible to use inorganicparticles. Here, as the inorganic particulates, particles of oxides,sulfides, hydroxides, nitrides, halides, carbonates, sulfates, acetates,phosphates, phosphites, organic carboxylates, silicates, titanates, andborates of elements of Group I, Group II, Group IV, and Groups VI to XIVof the Periodic Table and hydrous compounds or complex compounds,natural compounds, etc. of the same may be mentioned.

As the plasticizer, for example, tricresyl phosphate, trixylylphosphate, triphenyl phosphate, triethylphenyl phosphate, diphenylcresylphosphate, monophenyldicresyl phosphate, diphenylmonoxylenyl phosphate,monophenyldixylenyl phosphate, tributyl phosphate, triethyl phosphate,and other phosphate triester-based plasticizers; dimethyl phthalate,dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate,di-2-ethylhexyl phthalate, diisononyl phthalate, octyldecyl phthalate,butylbenzyl phthalate, and other phthalate ester-based plasticizers;butyl oleate, glyceryl monooleate esters, and other fatty acid-basicacid ester-based plasticizers; divalent alcohol ester-basedplasticizers; oxylate ester-based plasticizers; etc. may be used. Amongthese, phosphate triester-based plasticizers are preferable. Tricresylphosphate and trixylyl phosphate are particularly preferable.

Further, as specific examples of the plasticizer, squalane (C₃₀H₆₂,Mw=422.8), liquid paraffin (White Oil, ISO VG10, ISO VG15, ISO VG32, ISOVG68, ISO VG100, VG8, VG21, etc. defined in JIS), polyisobutene,hydrated polybutadiene, hydrated polyisoprene, etc. may be mentioned.Among these, squalane, liquid paraffin, and polyisobutene are preferred.

As an anti-static agent, stearyl alcohol, behenyl alcohol, and otherlong-chain alkyl alcohols, glyceryl monostearate, pentaerythritolmonostearate, and other fatty acid esters of polyhydric alcohols etc.may be mentioned, but stearyl alcohol and behenyl alcohol areparticularly preferable.

These compounding agents may be used mixed in two types or more. Theratio may be suitably selected within a range not detracting from theobject of the present invention. The amount blended may be suitablyselected within a range not detracting from the object of the presentinvention, but is normally in a range of 0.001 to 5 parts by weight,preferably 0.01 to 1 part by weight, with respect to 100 parts by weightof the thermoplastic polymer resin.

Molding Material

In the present invention, it is possible to use the above thermoplasticresin alone or a thermoplastic resin plus, as needed, the above softpolymer or compounding agents as the molding material. The moldingmaterial is normally kneaded, then extruded into strands in the moltenstate using a twin-screw kneader and cut into suitable lengths by astrand cutter for pelletization.

Light Guide Plate

The “light guide plate” in the present invention is a member for guidinglight of a light source entering a side end face in a direction parallelto the plate face and emitting it in a direction substantiallyperpendicular to the plate face. It is not limited in application, butmeans a light guide plate which is used in planar light source devicesused as backlights for laptop type, notebook type, book type, palmtoptype, and other type PCs, word processors, and other office automationapparatuses, wall hanging and other liquid crystal televisions. andother household electrical appliances, decorative electrical signboards,light tables, viewers, and other display devices.

Next, an explanation will be given of an embodiment of a light guideplate according to the present invention.

First, an explanation will be given of a planar light source device, inparticular an edge light type planar light source device.

For example, as shown in FIG. 1A, the edge light type planar lightsource device 10 is comprised of a light guide plate 100 for guiding andemitting light from a light source incident from a incidence face 100 ain a longitudinal direction, a light source 200 comprised of a coldcathode tube etc. arranged at least at one side face of the light guideplate (in the present embodiment, the incidence face 100 a), a lampreflector 300 arranged so as to surround the light source 200 forefficiently guiding to the light guide plate 100 the light of the lightsource which did not directly strike the incidence face 100 a of thelight guide plate 100, a light diffusion sheet 400 arranged at theemission face 100 b of the light guide plate 100 for diffusing the lightemitted from the emission face 100 c, and a reflection sheet 500arranged at the reflection face 100 c side of the light guide plate 100for returning the light leaking from the light guide plate 100 to thelight guide plate 100 once again.

As shown in FIG. 1B, the light guide plate 100 according to the presentembodiment forms a wedge shape so that the sectional shape becomesgradually thinner the further from the light source 200 so that lightemitted from the emission face 100 b becomes uniform as a whole. Notethat the “light guide plate” in the present invention has a thickness ofthe incidence face 100 a of not more than 5 mm, preferably 0.1 to 4 mm,more preferably 0.3 to 3 mm and a thickness of the nonincidence face 100d preferably not more than 4 mm, more preferably 0.05 to 3 mm, stillmore preferably 0.1 to 2 mm. Further, the ratio of area of the incidenceface 100 a and the emission end face 100 b is, based on theformer/latter, 1/5 to 1/500, preferably 1/10 to 1/400, more preferably1/15 to 1/300. Further, greater effects can be expected in a light guideplate having a length of the diagonal of the emission face 100 b of atleast 10 inches, preferably at least 14 inches.

As shown in FIG. 1C, in this embodiment, it is possible to use a moldwhich can give a light guide plate which gives the back face (reflectionface 100 c) of the light guide plate 100 a pattern comprised ofV-grooves 1001 in a gradually increasing density or deeper depth fromthe incidence face 100 a side of the light guide plate to thenonincidence face 100 d side.

The pitch (Pc) (see FIG. 1D) between adjoining V-grooves 1001 in thepresent embodiment is 10 to 5000 μm, preferably 30 to 1000 μm, morepreferably 50 to 500 μm. Further, the height H of the V-groove 1001 is10 to 5000 μm, preferably 3.0 to 1000 μm, more preferably 50 to 500 μm.Further, the pitch (Pc) at the nonincidence face 100 d side of the lightguide plate 100 between V-grooves 1001 is preferably 0.5 to 50% smallerthan the pitch (Pc) at the incidence face 100 a.

Molding Method

As the method for molding the above light guide plate, it is sufficientto use a conventionally known molding method. For example, injectionmolding, press molding, extrusion blow molding, injection blow molding,multilayer blow molding, connection blow molding, double-wall blowmolding, draw blowing, vacuum forming, rotational molding, and othermolding methods may be mentioned, but the preferred method is meltmolding (for example, hot press molding or injection molding). Morepreferable is injection molding from the viewpoint of the moldabilityand productivity. Below, the explanation will be given taking as anexample the case of producing a light guide plate by injection molding.

Injection Molding

In the present embodiment, an explanation will be made of the processfor production of the above light guide plate 100 by a screw typeinjection molding machine.

The screw type injection molding machine, as shown in FIG. 2A, iscomprised of a hopper 1, a heating cylinder 2, a screw 3, a mold 4, andan injection cylinder 5. Note that the process of molding of the presentinvention is not particularly limited so long as it is suitable formolding a thin-walled and a large screen size.

(1) Charging of Molding Material and Plasticizing and Melting of Same

First, as shown in FIG. 2A, a hopper 1 is charged with a moldingmaterial comprised of the above-mentioned thermoplastic resin and otherpolymers, various compounding agents, and a filler mixed in inaccordance with need all mixed in a predetermined ratio, kneaded by forexample a twin-screw kneader, and pelletized. The charged moldingmaterial falls by its own weight in the heating cylinder 2 to contactthe screw 3 and is gradually sent to the front end of the heatingcylinder 2 by the rotation of the screw.

Therefore, it is desirable to control the temperature of the heatingcylinder 2. The melting temperature of the molding material differsdepending on the type of the thermoplastic resin used, but normally is150 to 400° C., preferably 180 to 360° C., more preferably 190 to 330°C., particularly preferably 200 to 300° C. Therefore, the temperature ofthe heating cylinder 2 is suitably determined so that the moldingmaterial melts well and the resin is not broken down by heat andexhibits a stable, high fluidity in the mold. By maintaining thistemperature, it is possible to reduce burn marks of the resin or moldingstrain. The temperature of the heating cylinder 2 may be controlled by ajacket or heater.

The speed of the screw 3 is suitably determined so that the moldingmaterial is homogeneously mixed.

(2) Accumulation of Molding Material and Retraction of Screw

The molding material plasticized and melted in this way is stocked in apredetermined amount at the front end of the screw 3. Along with theprogress in the plastization, the screw 3 is retracted by apredetermined distance so as to move away from the nozzle 21 at thefront end of the heating cylinder 2 in the heating cylinder 2. At thistime, it is preferably to apply a back pressure of 20 to 150 kgf/cm² atthe injection cylinder side in a direction suppressing the retractionmotion of the screw 3. By making the back pressure 20 to 150 kgf/cm², itis possible to enhance the effect of plastization and kneading of themolding material and possible to prevent the occurrence of bubbles andsilver streaks of the molding material.

By making the screw 3 retract a predetermined distance in the heatingcylinder 2, a predetermined amount of molding material is stocked nearthe front end nozzle 21 of the cylinder 2 and made the amount ofinjection of the molding material injected in the mold 4. The amount ofinjection is not particularly limited due to the size, thickness, etc.of the light guide plate. The control of the retraction distance issuitably determined by a not shown microswitch etc.

(3) Injection

Next, as shown in FIG. 2B and FIG. 2C, the injection cylinder 5 is usedto make the screw 3 advance at a predetermined speed toward the nozzle21 of the heating cylinder 2 to make the plasticized and molten moldingmaterial stocked near the nozzle 21 pass through the nozzle 21 and fillthe mold 4. After the elapse of a predetermined time, the screw 3 isretracted (see FIG. 2D).

At this time, the injection speed is preferably changed in three stages.That is, first, the screw 3 is made to advance toward the nozzle 21 at apredetermined speed V1 to push the molding material into the sprue andrunner. When starting to pass near the gate of the mold, the speed ofadvance of the screw 3 is reduced to the speed V2, then made a speed V3faster than the speed V1 of the start of advance. This speed V3corresponds to the injection speed. Specifically, the injection speedcorresponding to the speed V3 of advance of the screw 3 is preferablymade 10 to 1000 cm³/s in the present embodiment. If the injection speedis less than 10 cm³/s, it is difficult to obtain a thin-walled, largescreen size light guide plate with a high planar accuracy. Luminanceunevenness tends to easily occur. On the other hand, the upper limit ofthe injection speed is preferably determined within a range enablingcontrol of the fluidity of the molding material, but if the injectionspeed is too fast, the temperature of the molding material rapidly risesdue to the shearing force and is liable to become a cause of silverstreaks on the shaped article.

Further, the pressure applied to the molding material when injecting themolding material from the nozzle 21 (injection pressure) by making thescrew 3 move forward to the nozzle 21 side may be suitably determined bymainly the viscosity characteristic (fluidity) of the molding material,the shape or thickness of the shaped article, or the structure of themold 4.

The injection pressure is divided into two stages: the stage ofinjection of the molding material in the mold 4 (hereinafter referred toas the “injection pressure”) and the stage after the mold finishes beingfilled (hereinafter referred to as the “holding pressure”). Theinjection pressure gradually rises at the time of filling the moldingmaterial in the mold and then sharply rises and sharply falls reachingthe peak pressure when the mold finishes being filled. The pressureapplied inside the mold after that is the “holding pressure”.

The holding pressure is the pressure applied for a certain time afterthe mold is substantially filled by the injection pressure until thegate portion of the mold 4 completely cools and solidifies. The lowerlimit is at least 100 kgf/cm², preferably at least 120 kgf/cm², morepreferably at least 150 kgf/cm². By making the holding pressure at least100 kgf/cm², the occurrence of whiskers at the light guide plate of theshaped article is prevented, the mold shrinkage factor can be madesmall, and a light guide plate superior in dimensional accuracy can beobtained. On the other hand, the upper limit of the holding pressure ispreferably determined within the range of the clamping pressure of themold. If the holding pressure exceeds the clamping pressure of the mold,the mold is liable to open during the cooling. Therefore, the holdingpressure is not more than 2000 kgf/cm², preferably not more than 1500kgf/cm², more preferably not more than 1200 kgf/cm².

In the present embodiment, the peak pressure is 95 to 15% of the holdingpressure, more preferably 90 to 40%, most preferably 80 to 60%. If setin this range, it is possible to prevent filling defects (short shots)in the mold 4 and increase the density of the light guide plate of theshaped article and possible to keep the mold shrinkage factor low, sopossible to obtain a high precision light guide plate. Further, it ispossible to suppress the occurrence of excess burrs in the shapedarticle and prevent the occurrence of deformation occurring due toexcessive internal stress remaining in the shaped article and possibleto avoid difficulty of mold release due to over packing in the mold 4and thereby prevent damage to the mold.

The nozzle size of the injection molding machine is determined so thatthe molding material does not decompose by heat, but in the presentembodiment if using a thermoplastic resin containing an alicyclicstructure as a molding material, it is possible to set the nozzle sizesmaller than in the past.

Further, as a preferable method of molding, use is made of a mold havinga value of a ratio S/L (mm²/mm) of the sectional area S of the gate andthe maximum flow length L in the cavity of the molding material (moltenresin) of at least 0.1, preferably at least 0.2. If the value of SL(mm²/mm) becomes less than 0.1, the mold transferability becomesinsufficient and luminance unevenness easily occurs.

The type of the gate is not particularly limited, but a so-called slitgate forming an elongated shape (also called a flat gate or film gate)is preferable.

The length of the short side of the gate in cross-section is normally 5to 100%, preferably 10 to 100%, particularly preferably 20 to 100%, withrespect to the thickness of the light guide plate. Specifically, it is0.2 to 2.5 mm.

The length of the long side of the gate in cross-section is normally 10to 100%, preferably 20 to 80%, with respect to the length of the side ofthe light guide plate. The length of the gate land is not particularlylimited, but normally is not more than 3 mm.

The area of the gate is, in terms of the ratio with the area of the sideface of the wedge shape having the gate, 1:2 to 1:15, preferably 1:2.5to 1:10, more preferably 1:3 to 1:5. By injecting the molding materialfrom this portion at this time, the fluid characteristics of thematerial in the mold are improved, flow marks and whiskers areprevented, no gate marks remain at the light reflection face of thelight guide plate, and luminance unevenness is difficult to occur, sogate cutting also become easy.

The gate is usually provided at the portion corresponding to the sideface (thickness portion) of the light guide plate. In particular, it ispreferable to provide it at the portion where the maximum flow length Lin the cavity of the molten resin becomes shorter in the portioncorresponding to the side face of the light guide plate. In the lightguide plate, if the gate is arranged at the portion corresponding to thelight incident face, gate marks sometimes remain at the light incidentpart. (thickest part), so in this case polishing or other aftertreatment is necessary after the light incident part is removed from themold. Therefore, it is preferable to arrange the gate at the sideopposite to the light incident part (thinnest part) or the side face.

Note that it is also possible to use a plurality of molds. In this case,it is preferable to arrange the gate to be as symmetrical as possiblewith respect to the sprue.

In the present embodiment, as shown in FIG. 3A and FIG. 3B, injectionmolding is performed arranging the gate at the side face of the lightguide plate 100 at the light incident face side from near the center sothat marks 600 corresponding to the gate remain at the emission face 100b side.

Further, as another preferable method of molding, the molding materialis filled in a mold clamped by a mold clamping force of 50 to 250 tons,preferably 60 to 230 tons, at an injection filling pressure of 50 to 600kgf/cm², preferably 100 to 400 kgf/cm², then the mold clamping force israised to 300 to 500 tons, preferably 350 to 470 tons for molding. Thatis, both the mold clamping force at the time of filling the moldingmaterial and the injection filling pressure are made smaller and themold clamping force after filling the resin is raised.

The mold clamping force may be adjusted by a known mold clamping method.For example, the toggle method and direct pressure method may bementioned. Normally, if the mold clamping force is made smaller, burrsoccur more easily. In this case, the holding pressure is normally made600 to 1100 kgf/cm², preferably 650 to 1050 kgf/cm².

The mold temperature is preferably set to a range from a temperature 10°C. lower than the glass transition temperature of the resin to be filledin the mold (molding material) to a temperature 40° C. higher than theglass transition temperature of the resin, more preferably a range fromthe glass transition temperature of the resin to a temperature 20° C.higher than the glass transition temperature of the resin. By making themold temperature this range, the light guide plate can be obtainedwithout any transfer defects.

(4) Cooling and Solidification of Molding Material

The molding material filled in the mold 4 is held for a certain time inthe mold 4 for cooling and solidification.

The cooling time may be suitably changed according to the cylindertemperature, mold temperature, thickness of the shaped article, etc. Ifthe cooling time is extended, it is possible to reduce the deformationof the shaped article, but this ends up lengthening the cycle time andmakes release of the shaped article from the mold difficult. On theother hand, if the cooling time is shortened, the solidification of theshaped article becomes insufficient and therefore deformation of theshaped article or deterioration of the dimensional stability ends upbeing caused. Therefore, it is necessary to determine the optimalcooling time taking into consideration these facts as well. Usually, itis about 1 to 15 minutes.

(5) Extraction of Shaped Article

After cooling in the mold for a certain time in this way, the mold isopened and the shaped article (light guide plate 10) is removed,whereupon one cycle of the molding process is completed (see FIG. 2E).This cycle may be performed by either manual operation or automaticoperation.

Embodiments of the present invention were explained above, but thepresent invention is not limited to these embodiments and may be workedin various manners within the range not exceeding the gist of thepresent invention.

EXAMPLES

Below, the present invention will be described in further detail withreference to production examples, examples of the invention, andcomparative examples. The present invention however is not limited tothese examples. Further, in the production examples, examples of theinvention, and comparative examples below, the parts and percentages arebased on weight unless specifically stated otherwise.

The methods of measuring the various physical properties in thefollowing Production Examples 1 to 6, Examples 1 to 6, and ComparativeExample 1 were as follows.

The “refractive index” was measured based on ASTM-D542 at 25° C.

The “glass transition temperature (Tg)” was measured based on JIS-K7121.

The “melt flow rate (MFR)” was measured based on JIS-K6719 a load of2.16 kgf at 280° C. The diameter of a hole of the die was 2.095±0.03 mm,while the distance of movement of the piston was made 25.0±0.25 mm.

The “50% breaking energy of the drop-weight test” was obtained byinjection molding a 3 mm thick plate and measurement based on JIS-K-7211in an atmosphere of a temperature of 23° C. and a relative humidity of50% dropping a missile-shaped weight of a radius of ¾ inch on the plate.

The “transparency” was measured by measuring the light transmittance (%)while continuously changing the wavelength in a range of 400 to 900 nmby a spectrophotometer (Model U-30 made by Nippon Bunkosha) and definingthe minimum transmittance as the light transmittance of the light guideplate. The higher the light transmittance, the better the transparency.

The “appearance and moldability” was determined by checking if there arebubbles, voids, or other defects in the light guide plate obtained bysight or checking if the shapes of the V-grooves have been transferredwell and evaluated by the following judgement criteria:

VG (very good): good transfer of shapes of V-grooves

G (good): No problem in molding in transfer of shapes of V-grooves

F (fair): bubbles, voids, burrs, and other defects partially observedand gaps or short shots partially observed in transfer of V-grooves

P (poor): bubbles, voids, burrs, and other defects observed and gaps orshort shots observed in transfer of V-grooves

The “luminance unevenness” was obtained by measuring the luminance atthree spots (vertical direction) at equal intervals at each of the thickpart and thin part of the face of the light guide plate (rectangularface 1.5 cm inside from the periphery of the face of the light guideplate) using a luminance meter (BM-7, made by Topcon Co.), calculatingthe luminance unevenness (%) by (minimum value/maximum value)×100, andevaluating the results by the following judgement criteria:

VG (very good): 88% or more

G (good): 85% to less than 88%

F (fair): 82% to less than 85%

P (poor): less than 82%

The “heat resistance” was evaluated by measuring the dimensional changesdue to changes in the environment (temperature changes). A light guideplate is normally used for a long time under irradiation by a lightsource, so dimensional changes due to temperature often become problems.Therefore, the dimensional change after holding a light guide plate in agear oven at 100° C. for 24 hours was measured as a representativecharacteristic and evaluated by the following judgement criteria:

VG (very good): dimensional changes of not more than 0.1%

G (good): dimensional changes of over 0.1% to 0.3%

F (fair): dimensional changes of over 0.3% to 1.0%

P (poor): dimensional changes of over 1.0%

The “mechanical strength” was evaluated by the impact resistance by adrop test. A ¾ inch radius missile-shaped weight (weight 10 g) wasallowed to naturally drop from a height of 50 cm on the same positionsof 10 prepared light guide plates. The occurrence of cracks or fractureswas examined. The evaluation was conducted by the following judgmentcriteria:

VG (very good): cracks or fractures in zero out of 10 samples

G (good): cracks or fractures in one to three out of 10 samples

F (fair): cracks or fractures in four to six out of 10 samples

P (poor): cracks or fractures in seven or more out of 10 samples

Production Example 1

Bicyclo[2,2,1]hept-2-ene (hereinafter referred to as “NB”) (118 kg) wasadded to a reaction vessel charged with 258 liters of cyclohexane atordinary temperature in a flow of nitrogen gas and agitated for 5minutes. Triisobutylaluminum was added to a concentration in the systemof 1.0 ml/liter. Next, ethylene was circulated, with agitation, atordinary pressure to make the system an ethylene atmosphere. Theautoclave was held at an inside temperature of 70° C. and pressurized byethylene to an inside pressure of 6 kg/cm² by gauge pressure. This wasagitated for 10 minutes, then 5.0 liters of a toluene solutioncontaining isopropylidene(cyclopentadienyl)(indenyl)zirconium dichlorideand methylalmoxan prepared in advance was added to the system so as toinitiate the copolymerization reaction of ethylene and NB. Theconcentration of the catalyst at this time was 0.015 mmol/liter ofisopropylidene(cyclopentadienyl)(indenyl)zirconium dichloride to theentire system. The concentration of methylalmoxane was 7.5 mmol/liter.

During the polymerization, ethylene was continuously fed into the systemto hold the temperature at 70° C. and the internal pressure at 6 kg/cm²in gauge pressure. After 50 minutes, the polymerization reaction wasstopped by addition of isopropyl alcohol. After the depressurization,the polymer solution was taken out, then brought into contact with anaqueous solution comprised of 1 m³ of water plus 5 liters ofconcentrated hydrochloric acid in a 1:1 ratio under strong agitation tocause the catalyst residue to move to the aqueous phase. The contactmixture was allowed to stand, then the aqueous phase was separated andremoved and the remainder rinsed twice to purify and separate thepolymerization solution phase.

The reaction solution was passed through a guard filter, then removed ofthe solvent and monomer and other volatile components by direct dryingusing a centrifugal thin film continuous evaporation drier. The obtainedmolten resin was pelletized by a melt extruder to obtain a copolymer (A)of ethylene and NB.

The weight average molecular weight Mw of the ethylene-NB copolymer (A)obtained in this way measured converted to polyisoprene by a GPC (gelpermeation chromatograph) using cyclohexane as a solvent was 38000, themolecular weight distribution Mw/Mn was 2.37, the MFR of the polymer was55 [g/10 min.], the 50% breaking energy was 0.63 J, the glass transitiontemperature Tg was 140° C., the refractive index was 1.53, and the NBcontent calculated by ¹³C-NMR was 53 mol %.

Production Example 2

The same procedure was followed as in Production Example 1 other thanmaking the reaction time 46 minutes to obtain an ethylene-NB copolymer(B) having an MFR of 65 [g/10 min.], a 50% breaking energy of 0.48 J, aTg of 141° C., a refractive index of 1.53, and an NB content of 53%.

Production Example 3

The same procedure was followed as in Production Example 1 other thanmaking the reaction time 20 minutes to obtain an ethylene-NB copolymer(C) having an MFR of 178 [g/10 min.], a 50% breaking energy of 0.31 J, aTg of 141° C., a refractive index of 1.53, and an NB content of 55%.

Production Example 4

The same procedure was followed as in Production Example 1 forpolymerization other than adjusting the internal pressure by theethylene to become a gauge pressure of 6.4 kg/cm². The obtainedethylene-NB copolymer (D) had an MFR of 52 [g/10 min.], a 50% breakingenergy of 0.19 J, a Tg of 123° C., a refractive index of 1.53, and an NBcontent of 43%.

Production Example 5

The same procedure was followed as in Production Example 1 other thanmaking the reaction time 17 minutes to obtain an ethylene-NB copolymer(E) having an MFR of 203 [g/10 min.], a 50% breaking energy of 0.10 J, aTg of 142° C., a refractive index of 1.53, and an NB content of 53%.

Production Example 6

The same procedure was followed as in Production Example 1 forpolymerization other than adjusting the internal pressure by theethylene to become a gauge pressure of 6.8 kg/cm². The obtainedethylene-NB copolymer (F) had an MFR of 53 [g/10 min.], a 50% breakingenergy of 0.03 J, a Tg of 105° C., a refractive index of 1.53, and an NBcontent of 33%.

Examples 1 to 6

0.2 part of the phenol-based antioxidantpentaerythrityl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)and 0.4 part of the hydrogenated styrene-butadiene-styrene blockcopolymer (Tuftec H1051 made by Asahi Kasel, crumbs, refractive index of1.52 at 30° C.) were mixed in 100 parts of each polymer obtained inProduction Examples 1 to 6 and kneaded by a twin-screw kneader, then thestrands (strand shaped molten resin) were passed through a strand cutterto obtain a pellet- (granular) shaped molded material. These pelletswere injection molded to prepare light guide plates A to F. The moldingconditions of the injection molding were the use of an injection moldingmachine of Model IS450 made by Toshiba Machinery, a mold temperature of60° C., a cylinder temperature of 310° C., a nozzle temperature of 260°C., an injection pressure of 1000 kgf/cm², a holding pressure of 800kgf/cm², a mold clamping pressure of 1200 kgf/cm², an injection speed(corresponding to screw speed of advance) of 40 cm³/s, a screw backpressure of 70 kgf/cm², and a screw speed of 30 rpm. Further, the timefrom the start of filling into the mold to the end of filling was 1second.

The obtained light guide plate, as shown in FIG. 1A and FIG. 1B, was awedge shape having a thickness at wide end (100 a side) of 2.4 mm, athickness of the narrow end side (100 d side) of 0.5 mm, a length fromthe wide end to the narrow end side of 180 mm, a length along the axialdirection of the linear light source of 320 mm, that is, a 14.5 inchessize, and a gradually decreasing thickness in the direction from thewide end side to the narrow end side (direction substantiallyperpendicular to the center axis of the linear light source). At thetime of mold release, no short shots or burrs and no cracks in theshaped article were observed in the shaped articles of Examples 1 to 4and 6 using the ethylene-NB copolymers (A) to (D) and (F). On the otherhand, for Example 5 using the ethylene-NB copolymer (E), while thetransfer of the V-grooves was good, since the reaction time at the timeof production of the resin was short, some burrs occurred. The lightreflection face side of the light guide plate is formed with V-groovesbecoming gradually denser the further from the wide end side of thelight guide plate to the narrow end side. The V-groove had an apicalangle of 110°, a pitch near the light source of 0.3 to 1.5 mm, and apitch near the narrow end of 0.03 to 0.06 mm. The depth of the groovewas made a uniform one of about 80 μm. Further, the transferability ofthe V-grooves near the narrow end was good. The gate shown in FIG. 3Aand FIG. 3B is positioned at the side close to the light incident facefrom the substantial center portion of the side of the emission face.The gate length was 70 mm and the gate thickness 2 mm.

The existence of bubbles on the surface of the light guide plate waschecked by sight, whereupon it was found that there were no bubbles onthe surface and the appearance was excellent. Further, the total lighttransmittance of the light guide plate was measured. The result was thatthe transparency was all excellent. Further, the mechanical strength wasevaluated using this light guide plate, whereupon it was confirmed thatthe impact resistance was excellent for Examples 1 to 5. For Example 6,however, due to the large ethylene content, a slight decline in themechanical strength was observed.

A reflection tape of Model RF188 made by Tsujimoto Denki Seisakusho wasadhered to the side end face of the light guide plate obtained in thisway other than the light incident face. A cold cathode tube of a tubediameter of 2.4 mm made by Harrison Electric was placed at the shortside light incident end. The area around the tube and the light guideplate incidence part was covered by a reflector of Model GR38W made byKimoto Co. Further, a light diffusion sheet of Model PCMSA made byTsujimoto Denki Seisakusho was placed at the emission face of the lightguide plate, while a reflection sheet of Model RF188 made by TsujimotoDenki Seisakusho was placed at the reflection face of the light guideplate to prepare an edge light type planar light source unit. This unitwas used to evaluate the total light transmittance, luminanceunevenness, and heat resistance. The results are summarized in Table 1.

Comparative Example 1

The same procedure was performed as in Production Example 1 except formaking the reaction time 62 minutes to obtain an ethylene-NB copolymer(F) having an MFR of 40 [g/10 min.], a 50% breaking energy of 0.95 J, aTg of 139° C., a refractive index of 1.53, and an NB content of 53%.This was molded under similar molding conditions as in Example 1 toobtain a wedge-shaped light guide plate having V-groove shapes.

The light guide plate obtained had the thin-walled part of the wedgeshape unfilled and exhibited transfer defects of the V-grooves. Themechanical strength was extremely good, but when evaluating the totallight transmittance, luminance unevenness, and heat resistance using aplanar light source the same as in Example 1, while the heat resistancewas extremely good, luminance unevenness occurred and the lightscattered in the light guide plate due to transfer defects of theV-grooves. As a result, the total light transmittance also fell. Notethat whether there were bubbles in the surface of the light guide platewas confirmed by sight, whereupon it was found there were bubbles in thesurface. The results are shown in Table 1.

TABLE 1 MFR Breaking NB Appearance (g/10 energy content TG Total lightLuminance and Heat Mechanical Resin min) (J) (mol %) (° C.)transmittance (%) unevenness moldability resistance strength Ex. 1Ethylene- 55 0.63 53 140 92 G G VG VG NB(A) Ex. 2 Ethylene- 65 0.48 53141 92 VG VG VG VG NB(B) Ex. 3 Ethylene- 178 0.31 55 141 92 VG VG VG VGNB(C) Ex. 4 Ethylene- 52 0.19 43 123 91 G G G G NB(D) Ex. 5 Ethylene-203 0.1 53 142 92 VG F VG G NB(E) Ex. 6 Ethylene- 53 0.03 33 105 89 G GG F NB(F) Comp. Ethylene- 40 0.95 53 139 90 P P VG VG Ex. 1 NB(G)

In the following Production Examples 7 to 9, Examples 7 to 9, andComparative Example 2, the various physical properties were measured bythe following methods:

The “refractive index”, “Tg”, “MFR”, “transparency”, “appearance andmoldability”, “mechanical strength (impact resistance due to droppingtest)”, and “heat resistance (where, residence time in gear oven is 720hours)” were measured in the same way as in Examples 1 to 6.

The “hydrogenation rate” was calculated by measurement of the ¹H-NMR.

The “front luminance” was obtained by placing a diffusion sheet (100MX,made by Kimoto Co.) at the emission face of the light guide plateformed, turning on the lamp, holding the state for 1 hour, thenmeasuring the luminance at nine points at equal intervals at the longside and short side (vertical direction) of the light emission face ofthe light guide plate on which the sheet is placed and calculating theaverage value.

The “luminance unevenness” was measured in the same way as in Examples 1to 6 and evaluated by the following judgement criteria:

VG (very good): 92% or more

G (good): 88% to less than 92%

F (fair): 84% to less than 88%

P (poor): less than 84%

The “durability test under a high temperature and high humidityenvironment” was conducted by allowing a sample to stand in a hightemperature, high humidity tank of a humidity of 90% and temperature of80° C. for 1000 hours, rapidly taking it out into a room temperatureenvironment (outside tester), then investigating the turbidity after theelapse of several minutes (change in light transmittance). The lighttransmittance at 700 nm was measured by a visible UV spectrophotometer,the value of (light transmittance after test/light transmittanceimmediately after molding)×100 was calculated, and an evaluation wasconducted under the following judgement criteria.

VG (very good): 98% or more

G (good): 96% to less than 98%

F (fair): 94% to less than 96%

P (poor): less than 94%

Production Example 7

1.22 parts of 1-hexene diluted by 10 parts of cyclohexane, 0.11 part ofdibutyl ether, and 0.22 part of triisobutylaluminum were placed into areaction and mixed with 250 parts of dehydrated cyclohexane in anitrogen atmosphere at room temperature, then 100 parts oftricyclo(4,3,0,1^(2,5))deca-3,7-diene (hereinafter referred to as DCP)and 30 parts of a 0.70% toluene solution of tungsten hexachloride werecontinuously added over 2 hours while holding the mixture at 45° C. forpolymerization.

The adjusted polymerization reaction solution was transported as it wasto a pressure-resistant hydrogenation reactor, 10 parts of adiatomaceous earth-carrying nickel catalyst were added, and a reactionwas caused at 180° C. at a hydrogen pressure of 45 kgf/cm² for 10 hours.This solution was filtered by a filter provided with a stainless steelmesh using diatomaceous earth as a filtration aid to remove thecatalyst. The obtained reaction solution was poured into 3000 parts ofisopropyl alcohol with agitation to cause the precipitation of thehydrogenate. This was then recovered by filtration. Further, thefiltrate was washed by 500 parts of acetone, then dried in a reducedpressure drier set to not more than 1 torr and 100° C. to obtain 95parts of a ring-opening polymer hydrogenate (A)

The MFR of the obtained ring-opening polymer hydrogenate (A) was 54[g/10 min.], the ratio of the repeating units including an alicyclicstructure in the total polymer repeating units was 100 mol %, the TG was94° C., the refractive index was 1.53, the hydrogenation rate was 99.9%,the weight average molecular weight (Mw) obtained from high pressureliquid chromatography (converted to polyisoprene) using cyclohexane as atransport layer was 31500, and the molecular weight distribution (Mw/Mn)was 2.10.

Production Example 8

The same procedure was followed as in Production Example 7 other thanmaking the amount of addition of 1-hexene added 1.35 parts to obtain aring-opening polymer hydrogenate (B).

The MFR of the obtained ring-opening polymer hydrogenate (B) was 185[g/10 min.], the ratio of the repeating units including an alicyclicstructure in the total polymer repeating units was 100 mol %, the TG was93° C., the refractive index was 1.53, the hydrogenation rate was 99.9%,the weight average molecular weight (Mw) obtained from high pressureliquid chromatography (converted to polyisoprene) using cyclohexane as amobile phase was 19200, and the molecular weight distribution (Mw/Mn)was 2.08.

Production Example 9

The same procedure was followed as in Production Example 7 other thanmaking the amount of addition of 1-hexene added 1.40 parts to obtain aring-opening polymer hydrogenate (C).

The MFR of the obtained ring-opening polymer hydrogenate (C) was 259[g/10 min.], the ratio of the repeating units including an alicyclicstructure in the total polymer repeating units was 100 mol %, the TG was93° C., the refractive index was 1.53, the hydrogenation rate was 99.9%,the weight average molecular weight (Mw) obtained from high pressureliquid chromatography (converted to polyisoprene) using cyclohexane as atransport layer was 13500, and the molecular weight distribution (Mw/Mn)was 2.05.

Examples 7 to 9

The same procedure was followed as in Examples 1 to 6 to prepare lightguide plates other than using the ring-opening polymer hydrogenates A toC obtained in Production Examples 7 to 9, making the mold temperature80° C., and making the cylinder temperature 280° C. (Examples 7 and 9)or 290° C. (Example 8).

Each obtained light guide plate, as shown in FIG. 1A and FIG. 1B, had awedge shape having a thickness at the wide end (100 a side) of 2.2 mm, athickness of the narrow end side (100 d side) of 0.5 mm, a length fromthe wide end to the narrow end side of 190 mm, a length along the axialdirection of the linear light source of 250 mm, and a graduallydecreasing thickness in the direction from the wide end side to thenarrow end side (direction substantially perpendicular to the centeraxis of the linear light source). At the time of mold release, no shortshots or burrs and no cracks in the shaped article were observed.

The light reflection face side of the light guide plate is formed withV-grooves becoming gradually denser the further from the wide end sideof the light guide plate to the narrow end side. The shape of a V-groovewas made the same as in Examples 1 to 6. The shown in FIG. 3A and FIG.3B is positioned at the side close to the light incident face from thesubstantial center portion of the side of the emission face. The gatelength was 50 mm and the gate thickness 1.9 mm.

Further, the existence of bubbles on the surface of the light guideplate was checked by sight, whereupon it was found that there were nobubbles on the surface and the appearance was excellent. Further, thetotal light transmittance of the light guide plate was measured. Theresult was that the transparency was excellent in all cases. Further,the mechanical strength was evaluated using each light guide plate,whereupon it was confirmed that the impact resistance was excellent. Theheat resistance of each light guide plate obtained was also excellent.Further, the results of the durability test of the obtained light guideplate under a high temperature, high humidity environment were alsoexcellent.

The same procedure was followed as in Examples 1 to 6 using each lightguide plate obtained in this way to prepare edge light type planar lightsource units. The front luminance and luminance unevenness wereevaluated using these units. The above results are summarized in Table2.

Comparative Example 2

The same procedure was followed as in Production Example 7 other thanmaking the amount of addition of 1-hexene added 0.84 part to obtain aring-opening polymer hydrogenate (D).

The MFR of the obtained ring-opening polymer hydrogenate (D) was 15[g/10 min.], the ratio of the repeating units including an alicyclicstructure in the total polymer repeating units was 100 mol %, the Tg was95° C., the refractive index was 1.53, the hydrogenation rate was 99.9%,the weight average molecular weight (Mw) obtained from high pressureliquid chromatography (converted to polyisoprene) using cyclohexane as amobile phase was 42000, and the molecular weight distribution (Mw/Mn)was 2.20.

This resin was molded under the same molding conditions as in Example 7other than making the cylinder temperature 290° C. to obtain awedge-shaped light guide plate having V-grooves.

The obtained light guide plate was free of short shots at thethin-walled part of the wedge shape, but transfer defects of theV-grooves were observed. The mechanical strength, heat resistance, anddurability under a high temperature and high humidity environment of thelight guide plate were all extremely good, but the transparency fell.Further, when evaluating the front luminance and luminance unevennessusing a planar light source unit the same as Example 7, luminanceunevenness occurred and the front luminance also fell. Note that whetherthere were bubbles in the surface of the light guide plate was checkedby sight, whereupon it was found that there were bubbles in the surface.The results are shown in Table 2.

TABLE 2 Ratio of alicyclic Total Durability MFR structural light FrontAppearance under high (g/10 units TG transmittance luminance Luminanceand Heat Mechanical temp. and Polymer min) (mol %) (° C.) (%) (cd/cm²)unevenness moldability resistance strength high humidity Ex. 7 Ring 54100 94 92 1800 VG VG VG VG VG opening hydrate A Ex. 8 Ring 185 100 93 921860 VG VG VG VG VG opening hydrate B Ex. 9 Ring 259 100 93 92 1900 VG GVG G VG opening hydrate C Comp. Ring 15 100 95 91 1300 F P VG VG VG Ex.2 opening (bubbles) hydrate D

What is claimed is:
 1. A light guide plate, characterized by comprisingan incidence face into which light from a light source is introduced, anemission face intersecting with said incidence face, from which lightintroduced from the incidence face is emitted, and a nonincidence faceside facing to said incidence face side; and being obtained by meltmolding a soft polymer, and a thermoplastic resin containing alicyclicstructure having a melt flow rate of at least 50 [g/10 min.] under aload of 2.16 kgf at 280° C.
 2. The light guide plate as set forth inclaim 1, having a sectional shape becoming gradually thinner from a sideof said incidence face to a side of a nonincidence face.
 3. The lightguide plate as set forth in claim 2, wherein the length of a diagonal ofsaid emission face is at least 10 inches.
 4. The light guide plate asset forth in claim 2, wherein the thickness of said incidence face isnot more than 5 mm and the thickness of said nonincidence face is notmore than 4 mm.
 5. The light guide plate as set forth in claim 2,wherein a reflection face facing said emission face is formed withgrooves as a pattern of fine shapes.
 6. The light guide plate as setforth in claim 1, wherein said thermoplastic resin containing alicyclicstructure has a 50% breaking energy of at least 0.01 J in a drop-weighttest, measured for a 3 mm thick plate of the same using a missile weightof a radius of ¾ inch.
 7. The light guide plate as set forth in claim 1,wherein said thermoplastic resin containing alicyclic structure has aglass transition temperature of at least 70° C.
 8. The light guide plateas set forth in claim 1, wherein said thermoplastic resin containingalicyclic structure is a norbornene-base polymer.
 9. A method ofproducing a light guide plate, characterized by comprising an incidenceface into which light from a light source is introduced, an emissionface intersecting with said incidence face, from which light introducedfrom the incidence face is emitted, and a nonincidence face side facingto said incidence face side; and being obtained by melt molding a softpolymer, and a thermoplastic resin containing alicyclic structure havinga melt flow rate of at least 50 [g/10 min.] under a load of 2.16 kgf at280° C.
 10. The method of producing a light guide plate as set forth inclaim 9, wherein said melt molding is injection molding.